1. Technological Field
The described technology generally relates to a method for generating M demodulation signals, M being a strictly positive integer. The described technology also relates to a method for demodulating a signal to be demodulated by at least M signals obtained by implementing such a method, a device able to implement such a method for generating M demodulation signals, and a detection system comprising such a device.
2. Description of the Related Technology
The described technology applies to the field of the detection and analysis of at least one target by electromagnetic waves, for example within radar or lidar applications.
The target is for example a hard target or a diffuse target.
“Hard target” generally refers to a solid object.
“Diffuse target” generally refers to a gas or a mixture of gases, optionally including particles in suspension whose dimensions are of the same order of magnitude as the wavelength of the electromagnetic waves.
Such a detection is for example intended to measure physical properties relative to the atmosphere, to produce a wind map, or to obtain distance and/or speed measurements relative to a hard target.
Traditionally, an electromagnetic wave is emitted from a source to the target and diffused by the target in a diffused wave. Part of the diffused wave is collected and analyzed to deduce the desired characteristics of the target therefrom. Desirably, the analysis done on the collected wave is a spectral analysis. More specifically, rays are sought in the spectrum of the collected wave, the frequency of the rays being representative of a property relative to the target.
“Spectrum” of the signal refers to the spectral power density of that signal.
The frequency of the emitted wave generally being comprised between several gigahertz and several hundred terahertz, it is desirable to transpose the spectrum of the collected wave to low frequencies to perform the spectral analysis, for instance frequencies below several gigahertz, to allow processing by the usual measuring instruments so as to detect the previously described rays.
To that end, it is known to make the collected wave interfere with part of the transmitted wave, also called “local oscillator”, and to record the resulting beat signal, then to perform the spectral analysis step on that beat signal, generally in baseband, or around a predetermined low frequency equal to the difference between the carriers of the collected wave and the emitted wave.
However, the wave sources not being perfect, the wave generated by a given source experiences fluctuations over time, for example fluctuations in intensity and/or fluctuations of the time phase of the generated wave.
Due to these fluctuations, at a given moment the collected wave for example has a phase partially decorrelated from the wave emitted at that same moment, with part of which the collected wave is mixed. This decorrelation results, relative to the ideal case with no fluctuations, in an enlargement of the rays of interest in the spectrum of the beat signal, combined with a decrease of the intensity of the rays.
It is known to demodulate the beat signal by a predetermined reference signal, chosen based on the distance at which the target is located. The predetermined reference signal is suitable for partially compensating the fluctuations of the wave source, in particular its phase fluctuations.
Nevertheless, such a method is not fully satisfactory.
In fact, the reference signal is not suitable for compensating the actual fluctuations of the wave source over time. The compensation for the broadening of the rays of interest is therefore limited.